Stop 1. Santiago Peak Volcanics

Take College Avenue north (away from S.D.S.U.). Proceed to first traffic light, turn right (east) on Del Cerro Avenue and go two blocks to the stop sign at Madra Avenue. Turn left (north) and follow Madra Avenue 2.3 miles up and over the mountain to the entrance to Lake Murray Park. Follow road past baseball fields and park as close to the east-facing slope of Del Cerro as possible. Walk to large outcrops of the Santiago Peak Volcanics (SPV) above jogging road that encircles the lake.

This outcrop is typical of the SPV in the Del Cerro block and in the general San Diego area. Tuff-breccias are the most common rock type. The clasts consist mainly of plagioclase-rich porphyries, some with trachytic textures, plagioclase crystal fragments, and sparse quartz and quartz- bearing granitoid fragments. All SPV rocks have a hydrothermal or low-grade metamorphic overprint consisting of epidote, chlorite, white mica, and calcite.

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